The digital video market is among the earliest markets to develop out of the emerging multimedia business. The applications of digital video will first appear in movie-on-demand (MOD) services, which enable viewers to call up particular movies or other video programs whenever they want to watch them. Most present day movie request systems are analog rather than digital having fixed movie start times.
Digital movie-on-demand programs may be provided from a centralized location for a large number of users or can be provided "downstream" at Local Exchange companies or Cable Companies. Movie-on-demand services are expected to be among the most popular interactive multimedia offerings on the electronic information superhighway.
A network providing movie-on-demand services, upon receipt from a MOD customer of a signal requesting to view a movie, must verify the request and set up necessary connections to a video storage server. To the customer, the MOD service should desirably operate in a manner similar to that of a typical VCR or laser disc player, providing features such as pause, fast forward, stop, and rewind. Ideally, the requested movie should be accessible immediately, or within one to two minutes from the time the request was entered.
The storage requirements for digital video are great. Storage requirements for a single movie, depending upon picture quality, compression ratio and length of the movie can vary from 1 gigabyte (GB) to 3 GB. Typically, a standard quality VHS movie 100 minutes long will require 1 GB of storage. Movies developed for High Definition TV may require storage capacities of 33 GB per movie. Early MOD systems that utilize this type of video/audio storage are targeted to accommodate approximately 1600 users, while later systems may provide service to 10,000 users per video server.
The video server must be able to access the video information delayed by one or two minutes and multiples thereof for the length of the movies and update all users in a specified real-time window. The delay allows customers to jump forward or backward in time, simulating the operation of a VCR or video disk player. In order to provide acceptable performance, many early video server implementations utilize large amounts of fast Dynamic Random Access Memory (DRAM); up to 60 GB per server at approximately $25/megabyte (MB).